1. Field of the Invention
This invention relates to signal transmission and particularly to systems and methods for encoding and decoding multiple transmitted signals.
2. Description of the Related Art
There are a variety of conventional methods for transmitting signals corresponding to different channels of information. One method uses a dedicated line for each channel of data and transmits in parallel. This method has the disadvantage of requiring multiple transmission lines which typically require more area and cost than using a single line.
Therefore, technologies have developed to transmit data from more than one channel over a single line. One convention method of accomplishing this is called time multiplexing in which each channel is assigned a specific time slot. For example, the encoder allocates times 0 to 20 for the first channel, times 20 to 40 for the second channel, and so forth. Since the times directly correspond to the channel, the decoder can identify and separate the channels according to the time of transmission.
In another conventional method, data from a channel is lead by a header or introductory data that identifies the channel of the data to follow. However, this method may delay some information and require additional signal capacity for the header.
A way of transmitting multiple channels on a single line without time multiplexing or addition of header information is desired.
A variety of signal format use signal redundancy in order to detect signal errors. The principles of the present invention use signal redundancy to transmit different channels of information (and more information) instead of using the signal redundancy to detect signal errors.
For example, in AMI coding, a three-state signal is produced having, for example, a positive state, a negative state, and a neutral state. A neutral state represents a 0 while the positive and negative states each represents a 1. A 1 is represented by a positive state (or negative state) if the most recent 1 was represented by a negative state (or positive state). An error is manifest by two consecutive positive states without an intervening negative state, or two consecutive negative states without an intervening positive state.
In an encoding method according to the present invention, a sampled binary state of a first input signal is obtained. A second input signal is sampled twice to obtain two sampled binary states. A transmitted signal initially has one of the three discrete states. The state is selected based on the sample binary states of the two input signals. The transmitted signal has a first of the three discrete states (e.g., ground) if the sampled binary state of the first input signal is a first of two binary states (e.g., a 0). The transmitted signal has a second of the three discrete states (e.g., a positive voltage) if the following two conditions are satisfied:
1) the sampled binary state of the first input signal is a second of two binary states (e.g., a 1), and
2) both sampled binary states of the second input signal are the same.
The transmitted signal has the third of the three discrete states (e.g., a negative voltage) if the following two conditions are satisfied:
1) the sampled binary state of the first input signal is a second of two binary states (e.g., a 1), and
2) the sampled binary states of the second input signal are different.
A decoding method decodes two binary signals from a multi-state signal having at least three discrete states. The first binary signal is provided with a signal portion having one of two binary states in response to the multi-state signal having a first discrete state. Otherwise, the first binary signal is provided with a signal portion having the other binary state. The second binary signal is provided with a signal portion having one of two binary states in response to the multi-state signal having the second discrete state. The second binary signal is provided with a signal portion having the other of the two binary states in response to the multi-state signal having the third discrete state. For example, the decoding method may transition the second binary signal or maintain the second binary signal at its previous state based on whether the multi-state signal has the second or third discrete states.
These methods allow an encoding of several signals into one multi-state signal, and for the decoding of the multi-state signal.